The present invention relates to a signal processing circuit for a color video printer which depicts a color print close in quality to a photograph on a printing paper on the basis of a color video signal.
Regarding prior-art color video printers, `IEEE Transactions on Consumer Electronics, Vol. CE-28, No. 3, August 1982` contains a paper entitled "Color Video Picture Printer" by Sohei Masuda, and `IEEE Transactions on Consumer Electronics, Vol. CE-31, No. 3, August 1985` contains a paper entitled "A COLOR VIDEO PRINTER WITH SUBLIMITATION DYE TRANSFER METHOD" by Yasunori Kobori et al. who are the inventors of the present invention.
As stated in the papers, with the prior-art video printers, a video signal of one frame is disjoined into R (red), G (green) and B (blue) signals which are the components of a color signal or into Cy (cyan), Ye (yellow) and Mg (magenta) signals which correspond to the color components of a coating material. The resulting signals are respectively converted into digital signals, which are first stored in dedicated semiconductor frame memories.
The respective color signals are read out and printed in a predetermined order. In this case, the frame memories and analog-to-digital converters (hereinbelow, termed A/D converters) for converting the color signals are driven at an identical clock frequency. Therefore, all the video signals can be uniformly stored in the frame memories within the frame period thereof (33 msec, in the NTSC format, and 40 msec. in the PAL format).
Since, however, each of the prior-art video printers requires A/D converters and frame memories for the respective color signals, the circuit arrangement thereof becomes complicated. It also has a problem in the aspect of cost because a large number of RAMs (random access memories) are needed as the frame memories, and at least three A/D converters are needed.